1. Field of the Invention
The present invention relates to surgical fastening devices used particularly in the field of orthopedic surgery for fusing two bones relative to each other and fixating portions of a broken bone together under compressive force. The present invention further relates to surgical implant devices utilized in procedures where rigid internal fixation in the fusion of two bones relative to each other and fixation of bone portions is desired.
2. Description of the Prior Art
Various orthopedic pins and fasteners have been devised to aid in properly compressing bones or portions of a fractured bone together so as to promote as much as possible their prompt fusion and primary healing. The most common internal fixation devices used to aid in the fusion of bones or fixation of a fractured bone include and rely upon screw fasteners which must be entered and advanced into the bone structures worked upon.
Internal fusion and fixation devices limit the motion between bones as do externally placed rods and bolts. The internal fusion and fixation devices though, allow earlier mobilization of the affected body part, more precise placement of fixation or fusion devices and reduces chance for infection entry through contamination from the external communication of fixation/fusion devices. Present-day techniques for Internal Fusion or Fixation of bones which employ the use of screws require a variety of lengths and diameters of screws which may be used alone or in conjunction with various plates, washers or wires. Screws fixate two pieces of fractured bone together by the compressive forces created through the shear of the screw threads embedded in the hard cortical bone and the compression of the head of the screw against the opposite surface of the bone. In fusing two adjacent bones, the screw threads anchor usually in softer cancellous bone. In fusing two bones or fixating portions of single bone, the threads anchor along the bore in the bone and resist displacement by the bone's intrinsic shear strength. Prior to inserting the screw, the surgeon must drill a bore through the bone and "tap" threads in the bore. After insertion of the screw, should the forces generated at the screw site be greater than the intrinsic strength of the "shear cylinder", the screw(s) may either explosively strip the thread from the bore or gradually loosen during the fixation period, failing to achieve the proper anchoring of the bone and accruing loss of compressive force. This is particularly evident in soft cancellous bone fusion where shear cylinder strength is very low.
Another group of devices which are primarily designed for use in tubular bones such as femur or tibia provide elongate fasteners which are of relatively narrow configuration when inserted into bone being worked upon and which operate to expand laterally or radially after being inserted to attain fixation in the bone. These devices are commonly classified or called "expanding nail devices". One such device is disclosed in my prior U.S. Pat. No. 4,409,974 for Bone-Fixating Surgical Implant Device issued in 1983.
Another group of devices as illustrated in my issued U.S. Pat. No. 4,632,101 entitled "Orthopedic Fastener" involves a surgical implant device for fixating bones and bone portions. The device is an elongate generally cylindrical unit surgically implanted within living bone portions, and includes a plurality of pivotally mounted struts which are deployed within the soft cancellous material of the bone distant from the fractured portion thereof. The struts are pivotally deployed radially outward from the unit until achieving an oblique angle and anchoring contact with the interior surface of the surrounding hard cortex of the distant portion of the fractured bone is established.
The expanding nail type devices discussed above are implant devices characterized by a tubular member having a plurality of triangular shaped arms. The implant device is inserted into a bore in the bone worked upon, across the fixation site, with the arms in a radially folded or collapsed position. Once inserted, the arms are caused to extend radially outward and are anchored against the cancellous material in the bone. The invention in my U.S. Pat. No. 4,632,101 is an improvement in this apparatus and also operates on the principle that the compressive force to hold the bone portions together is generated by inserting the device within the bone and the arms or struts are deployed within the bone to form anchors within the bone. Neither the expanding nail type devices or my Orthopedic Fastener provide an apparatus which have rotatable wings which lie beyond the end of the hollow cylinder.